Sex difference in the age-related decline of global longitudinal strain of left ventricle

Global longitudinal strain (GLS) is a valuable indicator of subclinical myocardial dysfunction. Whether the effect of aging on subclinical left ventricular dysfunction is sex-specific is not well documented. This study aimed to identify age-related changes in GLS according to sex in patients with a normal left ventricular ejection fraction (LVEF). In this cross-sectional, single-center cohort study in Korea, participants who underwent GLS measurement using 2D speckle-tracking echocardiography were retrospectively reviewed, and participants with normal LVEF (≥ 55%) without documented cardiovascular disease were included. Reduced GLS was defined as absolute values below 18%. Of 682 study participants (mean age, 58; female, 51.5%), 209 (30.6%) had reduced GLS. Females with reduced GLS were older than those with normal GLS (68 vs. 58 years, P < 0.001); with no difference of age in males (55 vs. 57 years; P = 0.265). Univariate analysis showed age to correlate significantly with reduced GLS only in female (r =  − 0.364; P < 0.001). In multivariable analysis, female > 66 years old had significantly higher risk of reduced GLS (Odds ratio 2.66; 95% CI 1.22–5.76; P = 0.014). In participants with normal LVEF, GLS decreased with age in females but not in males. Particularly, females aged 66 years and older had a significantly higher risk of reduced GLS. These findings suggest that GLS could be a valuable parameter for assessing subclinical cardiac dysfunction, especially in older females.


Transthoracic echocardiography
Echocardiographic images were acquired and measured according to the recommendations of the American Society of Echocardiography and European Association of Cardiovascular Imaging 16 .All transthoracic echocardiography and speckle tracking strain imaging were performed using the same ultrasound machine (GE Medical Systems, Milwaukee, WI, USA).
LV end-diastolic dimension, LV end-systolic dimension, and wall thickness were measured using M-mode, and M-mode echocardiography was conducted on parasternal views.LV mass index was calculated using a validated linear method and indexed to the body surface area.LVEF was measured using the Simpson's biplane method on apical 4-chamber and 2-chamber views.

Strain echocardiography
Speckle-tracking analysis was conducted during echocardiographic examinations by two experienced sonographers.All echocardiographic parameters were averaged over 3 cardiac cycles.The LV endocardial border was automatically traced using commercially available software (GE Medical Systems) and was manually adjusted by an experienced sonographer.GLS value was measured from the average of the apical 4-chamber, 2-chamber, and 3-chamber views.
We took the absolute value |x| for a simpler interpretation given the negative GLS values; hence, we described a more positive value as "reduced".Reduced GLS was defined as less than 18%, and normal GLS was defined as more than 18% 11,17,18 .

Statistical analysis
All statistical analyses were performed using SPSS statistics version 26.0 (IBM Corp., Armonk, NY, USA).Continuous variables are presented as means and standard deviations, and categorical variables are presented as frequencies and percentages.Comparisons between the two groups were conducted using Student's t-test for continuous variables and the Chi-square test for categorical variables.Univariate and multivariate binary logistic regression analyses were used to identify significant factors correlated with reduced GLS.Receiver operating characteristic (ROC) curve analysis was used to assess the correlation between sex and reduced GLS and to identify the optimal cutoff value of age for predicting reduced GLS risk.The choice of cutoff value was made using the concordance probability method.A comparison of the area under the curve (AUC) of reduced GLS between sexes was made to assess the influence of age on reduced GLS.Statistical significance was set at P < 0.05.

Baseline characteristics of total study participants
Of the 682 participants of this study, 209 (30.6%) had reduced GLS (Table 1).Participants with reduced GLS were predominantly males.Age did not differ according to GLS.Hypertension, diabetes, and obesity were more prevalent in participants with reduced GLS.Cholesterol levels and dyslipidemia were not significantly different between the normal and reduced GLS groups of participants, but serum triglyceride levels were higher in the reduced GLS group.The reduced GLS group took significantly more calcium channel blockers, renin-angiotensin blockers, and diuretics than the normal GLS group.

Echocardiographic findings in study participants
In all participants, mean GLS values of the reduced and normal GLS groups were 16.4 ± 1.35% and 20.2 ± 1.62%, respectively.LVEF was lower in the reduced GLS group than normal GLS group (65.6% ± 4.60% vs. 67.6%± 4.14%, P < 0.001).The reduced GLS group had a thicker LV wall, and higher LV mass index, and left atrial (LA) volume index than the normal GLS group.E/A ratio and septal E' velocity were lower in the reduced GLS group than normal GLS group (Table 1 www.nature.com/scientificreports/

Age-and sex-related differences
Baseline characteristics of the study participants, with respect to sex are shown in Table 2. Increasing age was associated with reduced GLS, but this effect was observed only in females; age difference between the groups with reduced and normal GLS was significant in females (68 vs. 58 years; P < 0.001) but not males (55 vs. 57 years; P = 0.265).In univariate linear correlation analyses, age was negatively associated with GLS in females (r = − 0.364; P < 0.001; Fig. 1A) but not males (r = 0.057; P = 0.303; Fig. 1B).The reduced GLS group had higher systolic and www.nature.com/scientificreports/diastolic blood pressures in both males and females, but more female had hypertension.Participants with reduced GLS showed higher diabetes prevalence and lower estimated glomerular filtration rate (eGFR) in females but not in males.The female in the reduced GLS group consumed more calcium channel blockers, beta-blockers, and renin-angiotensin blockers, while men consumed more diuretics.Age-and sex-related differences in the diastolic cardiac function are presented in Table 2. E/e' was significantly lower in the reduced GLS group in females, but not in males, and the LA volume index was significantly greater in the reduced GLS group in females, but not in males (Supplementary Figure ).
A Scatter plot was used to evaluate the correlation between age and GLS, and to compare the differences between males and females.GLS decreased with age in females; however, there was no significant correlation between age and GLS in males (Fig. 1).
Owing to age being statistically higher in participants with reduced GLS, ROC curve analysis was performed to compare the significance of age between sexes.The area under the ROC curve of reduced GLS in females was 0.729 (95% CI 0.66-0.80,P < 0.001, Fig. 2A).The area under the ROC curve of reduced GLS in males was 0.539 (95% CI 0.48-0.60,P = 0.222; Fig. 2B).The optimal cutoff age for predicting the risk of reduced GLS in females was 66.5 years.The sex-specific differences in GLS by age 66 years are shown in Fig. 3.At the age of 66 years, the difference in slope was evident in the scatter plot of age and GLS in females, but not in males.

Univariate and multivariate analysis showing clinical factors associated with reduced GLS compared by sex
Univariate and multivariate analyses were conducted with variables that showed significant differences between the two groups of females (Table 3).Hypertension (OR 3.69; 95% CI 1.52-8.97;P = 0.004) and low GFR_MDRD (Modification of Diet in Renal Disease) (OR 0.97; 95% CI 0.95-0.99;P = 0.006) were associated with reduced GLS, and age over 66 years was independently associated with reduced GLS (OR 2.66; 95% CI 1.22-5.76;P = 0.014) in females.
There were some statistically significant variables in the differences between reduced and normal GLS groups in males; however, these variables were not associated with reduced GLS in the multivariate analysis.

Discussions
In this study, we investigated the pattern of GLS change in patients with normal LVEF and the correlation between GLS and age according to sex.Although mean GLS was higher in females than in males (19.8% ± 2.29% vs. 18.2% ± 2.10%, respectively), GLS decreased significantly with aging only in females, and the cut-off age was 66 years.Therefore, GLS might help to assess longitudinal dysfunction with normal LVEF in older females.Moreover, this sex-specific reduced GLS may be a potential mechanisms for higher prevalence of HFpEF in older females.To the best of our knowledge, this is the first study to show a relationship between GLS and age and to offer the cut-off age value for reduced GLS in females with normal LVEF.

Normal LVEF and reduced GLS.
LVEF is widely used as a prognostic marker and has been a standard for classifying HF, but its use is limited in patients with HFpEF whose LVEF is preserved.GLS may be a method used in this setting.Previous studies suggested that GLS is reduced before LVEF is impaired 9 ; therefore, it has been proposed as an important parameter of early-stage or subclinical LV dysfunction 10,11 .
A prospective study demonstrated that reduced GLS was a strong predictor of HF admission among patients in stage A (asymptomatic at risk for heart failure) and B (asymptomatic with left ventricular dysfunction) HF.And patients in stage B HF with reduced GLS were significantly associated with a high risk of developing overt HF 19 .Moreover, GLS is a superior predictor of cardiac events and mortality than LVEF in early cardiomyopathies [20][21][22] .www.nature.com/scientificreports/Recently, decreased longitudinal systolic function has been suggested to be an important mechanism in HFpEF 4 and a meta-analysis reported significantly lower LV GLS in patients with HFpEF 12 .In this respect, LV GLS is expected to be helpful as a diagnostic method for HFpEF patients with a normal LVEF.

Previous studies of differences in GLS according to age and sex
Previous studies have reported differences in GLS according to advanced age and sex.In the Framingham study, echocardiographic measurements of LV myocardial strain were conducted in healthy adults (mean age, 63 years; 64% females) 13 .This study demonstrated that reduced values of GLS were associated with advanced age, and females showed greater GLS than males 13 .In the ARIC (Atherosclerosis Risk in Communities) study, LV mechanics in participants without prevalent heart failure (mean age 76 years, 61% females) were evaluated, and this study reported that advanced age was associated with reduced GLS and female showed greater GLS 6 .
In our study (mean age, 58 years; 51% females), however, there was no significant difference in age between participants with reduced and normal GLS, but mean GLS was higher in females than in males (19.8% ± 2.29% vs. 18.2% ± 2.10%, respectively) before considering age.These differences GLS by age might be owing to the different ages of the study participants and the proportion of females.In our study, although mean GLS value was greater in females than males, it significantly decreased with age only in females.Taken together, based on our results, a higher proportion of older females among the study participants might have affected the association between advanced age and GLS.Meanwhile, Park et al. determined the reference values for LV longitudinal strain using information from normal Korean patients (mean age, 47 years; 52% females) 14 .In this study, there were no significant differences in GLS between the different age groups, but females had higher LV GLS values than males 14 , which is in line with our results.However, with respect to age, the results were different when comparing LV GLS between age groups (< 40 years vs. > 60 years) in both sexes; younger females showed significantly higher GLS values than younger males, but in the older group, no significant differences were observed in this study.These results are somewhat similar with those of our study that there was no significant difference in age between participants with reduced GLS and normal GLS, and mean GLS was higher in females than in males (19.8% ± 2.29% vs. 18.2% ± 2.10%, respectively) before considering age.However, unlike the study by Park et al., our study demonstrated that females aged over 66 years showed significantly lower GLS.These different results might be owing to the different mean ages of the study participants; mean age in Park et al. 's study was 47 years, which implies that enrolled participants older than 66 years might not be enough to estimate the association between sex and GLS by age.
Based on these previous reports, considering age cut-off to interpret the GLS values differently by sex is significant and from this point of view, our results that older females showed significantly lower GLS than males, and that the cut-off age for predicting the risk of reduced GLS in female was 66 years, may deserve attention.

Why GLS decreases with age in female
Longitudinal function decreases with aging; therefore, myocardial twist may increase to preserve ejection fraction 6,23 .Compared to the myocardium of males, that of females exhibit lower myocardial turnover, apoptosis, fibrotic changes, LV volumes, and better contractile reserve 5,6,24 .To deliver sufficient cardiac output and satisfy tissue metabolic demand, better systolic function and more torsion may be necessary due to the significantly lower LV volume in females 6 .These differences could be explained by differences in sex hormones, such as estrogen, which may be advantageous in slowing the course of heart diseases 5 .Functional estrogen receptors (ERs [α and β]) were found in the ventricular myocardium, and estrogen binding has both genomic and non-genomic consequences 25 .Novotny et al. studied the protective effect of ERα in aged female rat hearts and found that ERα activation was effective in lowering necrotic and/or apoptotic cell death as well as ischemia-reperfusion damage in the aged heart 26 .Therefore, menopause is considered to have a relationship with reduced cardiac function and adverse LV remodeling.Several studies have shown that menopause adversely affects the myocardial performance index and velocities and Doppler aortic flow indices of LV systolic function 27,28 , thus estrogen level changes diminished LV systolic and diastolic functions.Maluleke et al. studied female rats, performed ovariectomy to cause menopause in half of rats, and compared cardiac function by conducting echocardiography in two rat groups.This study showed that ovariectomized rats had significantly decreased GLS but showed no significant difference after adjusting for BP and body mass.A lack of estrogen does not result in LV dysfunction, impaired myocardial deformation, or cardiac remodeling 29 .Our study also showed that age and hypertension were independent factors for reduced GLS in multivariable analysis.Taken together, the mechanisms of decreasing GLS in older females are not clearly understood; reduced cardioprotective effects such as estrogen fall in older females may cause GLS to decline, and traditional cerebrovascular diseases such as hypertension accompanied by menopause might cause cardiac dysfunction, which shows reduced GLS.

Clinical implications
HFpEF is more frequent in old age and females 30,31 and is significantly associated with cardiovascular morbidity and mortality 32 .Therefore, it is essential to detect HFpEF early in older females and provide proper management.
Our results demonstrated that GLS decreased with increasing age in females, and decreased GLS values were remarkable in females aged 66 years or older.This suggests that measuring LV GLS in older females, especially in those aged over 66 years, may provide information on LV dysfunction and allow clinicians to manage it early and adequately.To generalize our findings, further studies with larger populations are warranted.

Study limitations
This study has several limitations.First, this study included only Korean participants; therefore, it would not be valid to generalize the results to other populations.Second, this study found that increasing age in females is associated with decreasing GLS, but it could not analyze factors related to GLS due to lack of data on female factors, including menopause duration or hormone therapies that may have played a role.Third, this study was cross-sectional; therefore cardiovascular outcomes could not be compared between sexes in participants with reduced GLS and normal LVEF.Forth, due to the lack of information on NT-proBNP or heart failure symptoms, we were unable to analyze the association between reduced GLS and HFpEF in our study population.Finally, although we adjusted for several confounders and conducted a multivariate analysis, there could be possible unrecognized confounders that may have played a role in the observed associations.

Conclusions
In participants with normal LVEF, GLS decreased with increasing age in females, but not in males.In particular, the risk of reduced GLS was highly significant in females aged over 66 years.Our findings suggest that the assessment of LV function by GLS could be useful in adults with normal LVEF, especially in older females.

Table 2 .
Clinical characteristics and echocardiographic findings of study subjects by sex.GLS, global longitudinal strain.Numbers are mean ± standard deviation or n (%).GLS, global longitudinal strain.HTN : previous diagnosis, current antihypertensive medications or SBP and/or DBP > = 140/90.DM : previous diagnosis, current anti-diabetic medications or fasting blood glucose level > = 126 mg/dL.DL : previous diagnosis, current use of anti-dyslipidemic medications or LDL > = 160 mg/dL

Figure 2 .
Figure 2. Receiver operating characteristic curve of GLS for predicting age in both sexes.The area under the ROC curve was 0.729 in females and 0.539 in males.

Table 1 .
Clinical characteristics and echocardiographic findings of study subjects.

Table 3 .
Comparison between univariate model and multivariate model.GLS, global longitudinal strain.